1. Field of the Invention
The present invention relates to weight measuring systems and more particularly to spring scales using optical detectors for determining the displacement of a scale load support structure.
2. Brief Description of the Prior Art
Optical detection and magnification of deflection has been employed for the purpose of precise measurement in conjunction with spring weighing scales to provide accurate and simplified readings. Typical with prior optical detectors used in conjunction with such scales has been the use of Rhonchi rulings for generating optical interference patterns.
In general, such detectors comprised a pair of optical gratings, one movable with the scale load support and the other fixed to the scale frame. Movement of the scale load support resulting from the placement of a load on a scale pan provided modulation of a beam passing through the grating sets.
Many problems accompanied the use of optical gratings for such purposes. For example, alignment of optical systems was difficult and costly because clearance between the movable and fixed gratings had to be precisely controlled.
A further problem encountered with regard to such scales related to various nonlinearities of the scale load support deflection path which introduced certain error. For example, scale assemblies utilizing a parallelogram type linkage incorporating leaf springs such as that illustrated in U.S. Pat. No. 3,807,517 typically provided an arcuate travel path for load support deflection rather than a true vertical path. It should be appreciated that the nonvertical components of the load support deflection introduced error into the system which was significantly amplified by the optical detector.